Here I show a simple water level set up at an altitude of about 470 feet showing a distant mountain of 512 feet altitude dropping below the level line due to earth curvature. It also shows the horizon failing to rise to eye level, but instead dropping by more than half a sun/moon diameter, an amount consistent with the globe theory.
The level was set up at the Black Hill Lookout and trail head parking lot, in Morro Bay, California at an altitude a little above half way between the 440 and 480 foot lines on the topographic map. I estimate 470 feet including ladder height. It shows the level line towards Estero Point and the peak "Villa 2" which is marked 512 feet altitude on the topographic map. Despite Villa2 being higher than the location of the level, Villa2 falls well below the level line due to the downward curvature of the earth. This image also shows the horizon not rising to eye level, but falling .31 degrees, or more than half of the Sun/Moon diameter, below the level line. This is close to the predicted horizon dip of .36 degrees, from 470 feet altitude with refraction. The peak Villa2 is 12.32 miles from the level at bearing 307.9 degrees. The curvature drop without atmospheric refraction over 12.32 miles is 101 feet. Adjusted for standard refraction, the curvature drop should appear to be about 87 feet. The lattitude and longitude of the water level was 35.35825,-120.83359 Villa2 is in the Harmony Headlands state park near Estero Point, about halfway between San Francisco and Los Angeles at 35.467596,-121.006295. The camera was at maximum zoom of 36mm focal length for a 35mm equivalent focal length of about 200mm. At maximum zoom I previously measured the camera's pixel angular resolution at .0000336 radians per pixel. The ends of the water level were 70.1 inches between centers. The level tubing had an outer diameter of 15.5mm. The camera was about 13 yards behind the center of the level. This image was based on the file WaterLevelDistantMountainAndHorizonCurvatureDropDSCN0953.JPG of file size 8,276,946 bytes, taken 2017-10-23 10:28AM Pacific Daylight Time. It has been rotated slightly to level the horizon, a dotted line added, and cropped. This file, WaterLevelDistantMountainAndHorizonCurvatureDropDSCN0953.JPG, and WaterLevelApparatusDSCN0955.JPG have been placed in the public domain by me, the original photographer.
This water level is cheap and easy to reproduce. Just a couple dollars of tubing. Due to the limited accuracy of such a level, you should probably pick a distant target at least 7 miles (10km) or so away, and preferably at least 10 miles (16km) away to ensure sufficient drop to be easily visible. Use a topographic map to find a mountain, large building, mountain pass, road, or something in the distance equal or just a little higher in elevation than where you set up your level. If you don't trust the map elevations, you can go to the distant location with your level and sight back to your first location to see if your results are consistent.
If you are going to make a water level like this, be sure to keep the tube ends vertical in the front/back direction to prevent refraction shifting of the light if it passes through the clear tube walls at an angle. Being vertical in the side to side direction is not as important. The longer the tube is the more accurate it will be. When photographing the level, the camera should be 20 or 30 feet behind the level so the water level surfaces and the distant objects can both be nearly in focus. But being too far back reduces resolution in aligning the water surfaces. I think it is best to focus the camera on the water level rather than on the distant objects since the distant objects won't be very sharp anyway, and a sharp view of the level surfaces gives better accuracy. If your camera has a large diameter lens aperture like typical SLRs, then you probably should stop down the aperture to get a better depth of field so the level and distant objects will be in focus. I also recommend taking a picture with the near surface very slightly below the far surface so that the line of sight is actually very slightly down hill. That way if the distant mountain or horizon is still below even a slight down hill line, then you know it will be below a true level line.
The following are my attempt to upload full resolution images, unaltered from the camera, of the apparatus and location and of the leveled and cropped image above. These images were taken at about the same time and daylight brightness, but one looks darker because I used a darker exposure in hopes of getting a little better horizon contrast. I think it would have been better at normal exposure.